Institute of Solid State Physics
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SS22 WS22 SS23 WS23 SS24 WS24 Guidelines for Master Students
Mechanochemical synthesis and characterization of the metastable, nanocrystalline F ion conductor (BaxCay)La(1–x–y)F(3–x–y) Solid ion conductors are important materials as they find applications in many electrochemical devices, e.g., in lithium-ion batteries, fuel cells or in super capacitors.[1] Compared to their liquid analogues they are expected to feature a number of advantages such as longer lifetimes, higher energy densities as well as higher safety.[2] Hence, ongoing research is devoted to find new materials with enhanced ion conductivity properties.[1] Quite recently, fast ion conduction has been found for nanocrystalline binary alkaline earth fluorides such as (Ba,Ca)F2.[3] Here, we tried to modify overall F ion transport further by replacing Ba and Ca with trivalent cations such as La. Thus, nanocrystalline samples of (BaxCay)La(1–x–y)F(3–x–y) with varying stoichiometries were synthesized via high-energy ball milling the binary fluorides in a planetary mill under dry conditions. In general, mechanochemical routes allow the preparation of non-equilibrium compounds that, in many cases, cannot be prepared via conventional high-temperature or wet-chemical synthesis methods. Structural characterization of the compounds prepared was carried out using X-ray powder diffraction. Heat treatment of the samples clearly reveal their thermodynamic metastability. This behavior was further confirmed by differential scanning calorimetry, which was employed to investigate structural transitions as well as to monitor the phase separation taking place at elevated temperatures. Finally, variable-temperature conductivity spectroscopy was used to study anion transport properties of the quaternary fluorides synthesized. |
